autotools: add some missed hardening link flags
autotools: mark libimm32 as windows only and

add a quick hack for not trying to link plugins on platforms where they're not
needed. See TODO.
autotools: use debug by default

This was backwards before, it now mimics the legacy behavior.

In the legacy buildsystem, the builder had to specify 'qmake RELEASE=1'
explicitly. Now builders can use --disable-debug to get the same result.

Gitian has been updated to use --disable-debug.
autotools: make the gzip from make dist deterministic

Note: This doesn't make a tar -cz deterministic without 'tar --mtime=...'
autotools: final gitian cleanup

- Install pkg-config for win32 even though it's not used. This ensures that
  Linux/win32 share the same generated aclocal. Set the reference time to match
  Linux as well.

- Set TAR_OPTIONS to specify the reference time. Now that gzip does not insert
  timestamps, 'make dist' is deterministic (even between win32 and Linux)

- Don't use faketime for Linux now that it's no longer needed. It's only used
  for the final make in win32 due to the timestamp in the PE header that's
  added during the final link.

- Use make install-strip to copy the resulting binaries